Impedance cardiography (ICG) is used to derive various cardiac parameters based on the impedance of blood flowing through the heart. With ICG, historically four pairs of electrodes are attached to the patient, two pairs at opposing regions about the neck and two pairs at opposing regions about the front lower chest. One electrode of each pair is used to inject a pre-determined electrical current, which travels through a low resistance path in the body such as blood flowing from the heart. The other electrode of each pair detects a signal indicative of a change in impedance (thoracic electric bio-impedance) of the blood flowing from the heart during each heart cycle based on the change in impedance from the change in voltage induced by the injected electrical current.
Electrocardiography (ECG) is used to sense and record electrical activity of the heart. For a commonly used Wilson three-lead ECG, two electrodes are attached to opposing shoulder regions and a third electrode is attached to the front lower chest area. The different electrodes sense electrical activity of the heart during each heart cycle. Historically, difference signals, corresponding to differences between voltage measurements for pairs of electrodes, are generated and graphically presented as waves (e.g., on a display or paper) and provide information about the heart. This information can be used to identify electrical rhythms of the heart, including abnormal electrical rhythms, heart muscle damage, and/or other information.
When the above noted ICG and three-lead ECG configurations are used in conjunction, a relatively large number of electrodes (e.g., seven, or four electrode pairs for ICG and three separate and distinct electrodes for ECG) are affixed to the patient. With five and twelve lead ECG configurations, even more electrodes are attached to the patient. Moreover, cables are run from each electrode to the ICG and ECG monitoring apparatuses.